Today's KNOWLEDGE Share:adiabatic heating

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Today's KNOWLEDGE Share:

Do you know what "adiabatic heating" means when referring to Injection Molding ?


There's a bit of misunderstanding out there because there are two distinct aspects to consider.

"Adiabatic compression", the mere fact that polymers are locally quickly compressed at high P, leads to a temperature increase of abt. 5-10°C under 1000 b. This T increase relaxes back as you decompress. Just like in a perfect gas.


 

On the other hand, the very fast character of filling a cavity in I.M., leads to "quasi adiabatic conditions" for the heat transfer to the steel. As a result, any frictional heat generated by the shear (known as "shear-heating") turns into strong localized temperature increase in the high shear layers. Because there is almost no heat conducted out within that short time (precisely, what we call ADIABATIC conditions), one can quite accurately estimate total/average shear heating temperature increase from the flow pressure drop. A 1000 bar pressure loss (that is a direct energy measurement !) translates into abt. 40°C average increase in melt temperature.


Source:Vito Leo

Visit MY BLOG http://polymerguru.blogspot.com


#injectionmolding #plastics #polymerscience #plasticsindustry #adiabaticheating #shear #pressure

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